This product is made by Advanced Card Systems Limited and seems to be available in different layouts but hardware doesn't differ so much.

They are all using a PN532 NFC Controller chip and a ST7 microcontroler unit.

I've made some pictures of the designs I have seen in the wild, but there are probably more.

Feel free to send pictures of different designs you stumble on.

The current release of libnfc supports all firmware versions.

Important note: libnfc needs “CCID Exchange command” from PCSC-lite to work, plus PCSC-lite denies bogus firmware: >= 2.0 and < 2.07. You will need to configure PCSC in order to libnfc work correctly (please see Troubleshooting section in README file)

The ACR122 reader is also used in the touchatag project (formerly tikitag).

Unlike many other devices, you can order it from the e-store. A starter package for only $39.95 and this package contains:

• 1 ACR122 Reader,
• 10 stickers MIFARE Ultralight tags.

Important notes:

• These tags have a pre-defined read-only content which is almost but not fully compiliant to NFC Forum Type 2 Tag specifications,
• Even Touchatag is the simpliest device to obtain, this device have a poor support for emulation and P2P under libnfc.

At the moment, it seems libnfc can talk with all ACR122, please report success or failure.

The following versions were reported to work:

• ACR122U101: ACS ACR122 v1.01,
• ACR122U102: Tikitag v1.02,
• ACR122U102: Touchatag,
• ACR122U203: ACS ACR122 v2.03, PICC

On this picture, you can see PN532 chip (red circle) and a 8-bit MCU (the biggest chip).

This touchatag contains:

• NFC chip: PN532/104 model (no public datasheet available…)
• MCU: ST7SCR1E4M1 8-bit low-power, full-speed USB MCU with 16Kbytes Flash, 768 bytes RAM, smartcard interface and timer